Microwave duplexer



April 25, 1961 REINGOLD ETAL MICROWAVE DUPLEXER 2 Sheets-Sheet 1 Filed June 5. 1958 "II III INVENTORS IRVING REINGOLD BY L. ARTER f? ATTORNEY.

JOHN

April 1961 REINGOLD ETAL 2,981,901

MICROWAVE DUPLEXER Filed June 5, 1958 2 Sheets-Sheet 2 up FIG.4 1 F FIG. 5

5250 "U a: 3 m

I I I l 1 2650 2100 2150 2000 2050 2900 2950 2785 2790 2 2800 2805 ZBIO 2 I FREQUENCYmc FREQUENGYmc FIGS I I l 2100 2150 2500 2050 2900 2950 5000 FREQUENcYmc INVENTORS IRVING REINGOLD y JOHN L. CARTER ATTORNE.

2,981,901 IVIICROWAVE DUPLEXER., Irving Reingold, West Deal, and John L. Carter, Asbury Park, N.J., assignors to the United States of America i as represented by the Secretary of the Army Filed June 5, 1958, Ser. No. 740,175

'3 Claims. (Cl. 333-13) (Granted under Title 35, U.S. Code (l952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

This invention relates to microwave duplexers and more particularly to waveguide type duplexers utilizing ,TR tubes.

1 At relatively high power levels it has been found that conventional radar duplexers of either the branch or balanced type are not particularly effective in alleviating the problem. of mutual interference between nearby radar systems operating substantially in the same frequency band The duplexer in a pulsed radar system is essentially a microwave switch utilizing active elements commonly known as TR, pre-TR and ATR tubes. Such tubes are usually of two types, the broadband waveguide type and the cell-type. Conventional broadband fixed tuned types of TR tubesare generally designed forioperationat high power levels. Their selectively is relatively poor inasmuch as they willaccepta spurious or interfering signal at any frequency .within theirbandwidth. Tuneable waveguide types of TR tubes fhave somewhat better selectivity but not sufficiently better to alleviate the situation to any worthwhile degree. Narrow-band, cell-type, tuneableTR tubes, which are mounted in an external cavity,

. are generally incapable of satisfactorylong life operation at relatively higlr power levels. Some systems use wave- 1 guide filtersinor'der to eliminate spurious signals. 'While this approach has a desirable result in reducing interference, the filters usually add a degree of insertion loss operational standpoint.

tothe system which is oftenintolerablefrom the overall l the inherent limitations of eachtyp It is another object of the presentinvention'to provide an improved'waveguide' type duplexer tube arrangement capable of operation at relatively high, incident power levels with a relatively high degree of selectivity.

T It is still another object of the present invention to provide an improved waveguide type duplexer tube where- .in the dimensions are not critical for operation over a relatively wide band of frequencies. V t I In accordance with the present invention, the duplexer includes-an encapsulated resonant window structure adapt- 7 system are as indicated by the arrows.

2,981,901 Patented Apr. 25, 1961 of the coupling irises. By tuning the cell-type TR tube, the duplexer is made responsive to a selective frequency Within the prescribed band of frequencies.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings in which:

, Fig. 1 illustrates the duplexer structure in accordance with the present invention;

Fig. 2 is a cross-section taken along line 2-2 of Fig. '1 and illustrates the position of the TR tube with the cavity resonator; Fig. 3 is a cross-section taken along line 3-3 of Fig. 2, and

Figs. 4, 5 and 6 are a group of explanatory curves.

Figs. 1, 2, and 3 of the drawings illustrate a duplexer tube 10 which may be utilized in microwave pulsed radar systems employing either a branch type ora balanced type of duplexer arrangement. The input of the duplexer receptive to the incident energy and the output of the dupleXer which is coupled" to the receiver of the radar It is to be understood of course that the duplexer hereinbelow described is positioned in a duplexer system so that it functions primarily as the TR section of the duplexer system.

Referring now to Figs. 1 and 2 of the drawings, there is shown at 11 a rectangular frame portion made of metal, Kovar for example, having a resonant rectangular slot 12 for transmission of microwave energy. Hermetically sealed to the slot 12 is a sealed capsule 14, made of glass, which contains a well known gas-fill such as argon or argon pluswater vapor, at a pressure of 5-50' mm. of mercury and a quantity of quartz Wool indicated at 16. With the capsule 14 hermetically sealed to the slot, the combined structure provides an input encapsulatedresonant window structure which incorporates the functions of a pre TR tube and a resonant TR tube in one unit capable of operation over a relatively broadband at high power levels. The recovervtime and arc-loss characteristics of the encapsulated window structure are determined by the type of gas-filled used. While it is desirable to hold the arc-loss to a minimum, the

recovery time desired depends of course on the-system requirements in which the, encapsulated window is to be utilized; As shown, the encapsulated window structure is provided with a mounting flange member '18 jWhlCh lS adapted toi engage a similar flange member 20 gathered to the input end of a; rectangular waveguide sec- ,tion 22 having substantially the same cross-sectional dimensions 7 as that of' r ectangular frame portion 11.

The output end of waveguide section 22 is provided with a reduced rectangular aperture, or coupling iris 24 which functions as a"feed-through to a cylindrical cavity resonator 26 having a tuneable cell-type TR tube 28, a 11327 for example, centrally positioned therein. Such tuneable cell-type TR tubes are well known in the art and are described on pages 37-39 of Microwave Q 'Duplexers, volume 14 of'the MIT Radiation Laboratory ed to pass a prescribed band of microwave frequencies.

Also included is a cylindrical cavity resonator having a pair of oppositely aligned rectangularcoupling'irises and resonant to said band of frequencies. Included further is a tuneable cell-type TR tube mounted within the cavity.

resonator such that the cell-type TR tubeis adapted to be' selectively tunedover the prescribed band of microwave frequencies. In addition, there. is provided a first rectangular waveguide interconnectingone of said irises and Series. As'shown in Fig. 3,- the cell-type TR tube 28- is positioned transversely within cylindrical cavity 26 such that there is a maximum voltage across the --dis- :charge gap 3t) formed between the conical electrodes 32 and 32. The cell-type TR tube 28 is tuned by vary ing the gap spacing by means of a diiferentialscrew mechanism 3 3 that moves one of the cones in or out. The movement of the differential screw is accomplished by means of aknurled knob 34 which is aflixed to a -'rotatabl e'shaft member 35 which, in'turn,-is afiixedto ,one end of the ditferentialscrew 33, the other end of the differential screw being affixed to 'conical'electrode; v 32. To permit the tube 28 to be connected intocylindrical cavity resonator 26, this cavity resonator is split in two halves along a diametral plane. With tube 28 in position, both halves of the cavity are aligned by means of pins 36 and locked in this position by means of threaded clamping nuts 38 which are adapted to engage external annular threaded flanged portions 40 extending laterally from the outer walls of cylindrical cavity resonator 26. It is to be understood of course that the cones 32 and 32 are sealed to maintain a low pressure region around the gap 30. This sealed portion is intermediate the circular flanges 4-2 which form part of cell-type tube 28. The combination of the celltype tube 28 and the cavity resonator 26 provides a high-Q element which can be selectively tuned through a relatively broadband of frequencies and also control the leakage power through the duplexer. For proper operation, the parameters of the cavity resonator 26 are chosen so that the tuning of the cell-type tube 28 is effective over the bandpass capabilities of the slot 12. A rectangular coupling iris 44 diametrically disposed with respect to iris 24 is provided in the wall of cylindrical cavity resonator 26 to function as a free-through therefrom to a rectangular waveguide section 46 adapted to be connected to a standard waveguide transmission line. For ease of construction, one-half the cavity resonator 26 and input waveguide 22 may be formed as one integrated structu e while the other half of cavity resonator 26 and ou put waveguide section 46 may be formed as another integrated structure.

To better understand the operation of the duplexer, reference is made to the curves shown in Figs. 4, 5, and 6. The bandpass curve of the encapsulated window structure is that of a typical broadband pre-TR tube and is shown in Fig. 4. e For one particular band of operation the dimensions of the encapsulated window were so chosen that it easily covered the frequency range of 2700 to 2900 megacycles. The average leakage through the encapsulated window was found to be in the order of 100 milliwatts and the recovery time was found to be less than 15 microseconds. Fig. 5 shows the bandpass curve of the cell-type TR tube 28 in the cavity resonator 26 which is dimensioned so that it is also resonant in the 2700-2900 megacycle range. Inasmuch as the loaded Q of such a cell-type TR tube and cavity resonator structure is quite high, the bandpass curve of the cell-type TR tube is quite narrow but can be tuned to resonance anywhere within the 2700-2900 megacycle region with approximately the same bandpass curvebeing achieved. The bandpass curve of the combined structure is shown in Fig. 6. This curve is representative of the bandpass curve of the entire structure when the cell-type tube 28 is tuned anywhere between 2700 and 2900 megacycl es. By tuning the celltype tube 26 ,the duplexer can bemade to selectively operate at a prescribed frequency between 2700 and 2900 megacycles.

Besides affording protection from interference from adjacent radars, the dupleXer hereinabove described was 5 found to have other advantages over existing TR tubes.

It provided operation at incident power levels considerably higher than that at which a cell-type high-Q TR tube could operate effectively. Also, the insertion loss was found to be lower than that of presently used combinations of TR tubes and pre-selector filters for allowing the same bandwidth.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A duplexer responsive to microwave frequency energy comprising, an encapsulated resonant window structure adapted to pass a prescribed band of microwave frequencies, a cylindrical cavity resonator having a pair of oppositely aligned rectangular coupling irises and resonant to said band of frequencies, a tunable cell-type TR tube mounted within said cavity resonator, said cell-type TR tube being selectively tunable over said prescribed band of microwave frequencies, and a rectangular waveguide terminated at one end by one of said irises, the other end of said rectangular waveguide being coupled to said encapsulated window structure.

2. The duplexer in accordance with claim 1 and further including a rectangular waveguide coupled to the other of said irises.

3. The duplexer in accordance with claim 1 wherein said encapsulated window structure comprises a rectangular frame portion having a resonant, slot therein, and a sealed capsule containing an argon gas-fill at a pressure within the rangeof 5-50 mm. of mercury hermetically sealed to said slot.

References Cited in the file of this patent UNITED STATES PATENTS.

Fiske Feb. 7, 1950 Lesch May 7, 1957 OTHER REFERENCES (1,948), pages 39-46 and 67-70 relied on. 

